[joshuacc]

Generally speaking, you'd use Angular with a backend framework.

Angular and other front-end frameworks are great for responding to user interactions extremely quickly, because often you don't have to go back to the server. And in addition when it does need to interact with the server, it is often faster to respond because it doesn't need to fetch anything but JSON data.

But that data needs to come from somewhere. And that's where Rails/Django/Play/Symphony/whatever are used.